Mechanical seal and method of forming a sliding surface thereof

ABSTRACT

A mechanical seal has a predetermined number of fine grooves formed on a sliding surface thereof, both ends of the fine grooves respectively reaching the outer peripheral end and the inner peripheral end of the sliding surface, part of the fine grooves being inclined forwardly and the remainder inclined rearwardly with respect to the relative rotational direction of the sliding surface. With those fine grooves it is intended to improve the sealing effect and the lubricating effect of the sliding surface. Also provided is a method of forming such a sliding surface.

BACKGROUND OF INVENTION

This invention relates to a mechanical seal.

Heretofore, as means for decreasing the amount of leakage in amechanical seal, there have widely been known a method wherein, withrespect to the sliding surface of a seat ring and that of a seal ringboth rings constituting a mechanical seal, a fluid film interposedbetween those sliding surfaces is made thinner by improving the surfaceaccuracy of the sliding surfaces, and a method wherein a spiral grooveis formed on the sliding surface and the fluid film is made thinner byutilization of the resulting pumping effect.

However, in both of the above conventional methods, the decrease of theamount of leakage results in increase in the generation of heat inducedby sliding motion, thus causing heat deterioration such as heatdeformation and wear on the sliding surface and in some cases furthercausing breakage of the seal such as cracking and foaming on the slidingsurface, and eventually the sealing durability deteriorates.

Thus, it has heretofore been considered very difficult to control bothsealing performance and sliding heat generation which are contrary toeach other, and to this end there have been adopted heat-resistantsliding materials for the foregoing seat ring and seal ring to increasethe safety factor, or a little increase in the amount of leakage hasbeen allowed.

As means for forming a sliding surface of a seat ring or seal ring inconventional mechanical seals, there have widely been adopted lapping,grinding, cutting and molding methods, and after application of thesemethods there is applied polishing, buffing, or a mechanical or chemicalsurface roughing.

However, although such conventional methods are somewhat effective inachieving their object, namely, the maintenance of sealing durability,they cannot specify the distribution ratio between a sealing surfaceportion and a lubricating surface portion of a sliding surface, andtherefore it has not yet been possible to properly control the amountleakage and the of heat generated on the sliding surface.

BRIEF SUMMARY OF INVENTION

This invention has been accomplished in view of the aforesaid problems.It is an object of this invention to provide a mechanical seal greatlysuperior not only in sealing performance but also in lubricatingperformance and further superior in sealing durability wherein theleakage of fluid is prevented by a sliding contact between a seat ringfixed to a housing and a seal ring fixed to a rotating shaft which isinserted through the seat ring, the seal ring being adapted to rotatetogether with the rotating shaft.

It is another object of this invention to provide a method of easilymanufacturing a mechanical seal capable of controlling both the sealingperformance or the amount of leakage and the lubricating performance orthe amount of heat generated.

The aforesaid objects of this invention can be attained by a mechanicalseal of a construction such that fine grooves are formed on the slidingsurface of either a seat ring or a seal ring so that both ends thereofrespectively reach the outer peripheral end and the inner peripheral endof the sliding surface and so that part of the fine grooves are inclinedforwardly and the remainder inclined rearwardly with respect to therelative rotational direction, and among the fine grooves, those in therelative rotational direction for performing a pumping action or sealingaction are formed predominantly, and by a method wherein the finegrooves of such a construction are formed by photo-printing the finegrooves on the sliding surface onto which has been applied aphotosensitive material in advance, or by stamping or printing with inksthe fine grooves on the sliding surface, followed by etching.

A brief summary of this invention has been given above, but the aboveand further objects and novel features of the invention will more fullyappear from the following detailed description when the same is read inconnection with the embodiments shown in the accompanying drawings. Itis to be understood, however, that the drawings are for purpose ofillustration only and are not intended to limit the scope of theinvention.

BRIEF DESCRIPTION OF DRAWING

FIG. 1 is a partially cutaway sectional view of a mechanical seal in amounted state according to one embodiment of this invention;

FIG. 2 is a front view of a sliding surface of a seal ring;

FIG. 3 is an enlarged front view of the principal part of the slidingsurface of the seal ring showing the state of movement of a sealingfluid;

FIG. 4 is an enlarged transverse sectional view of the sliding surfaceof the seal ring;

FIGS. 5 through 7 are each a front view of a sliding surface accordingto other embodiments of this invention;

FIG. 8 is an experimental graph showing the relationship between thenumber of fine grooves formed on a sliding surface and the amount ofleakage; and

FIG. 9 is a front view of a sliding surface according to a furtherembodiment of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

As shown in FIGS. 1 and 2, numeral 1 designates an external pressuretype mechanical seal with its principal parts illustrated on a largerscale. The seal is intended to prevent leakage of fluid (A) presentabout the outer periphery of the mechanical seal 1 by sliding contactbetween a seat ring 3 fixed to a housing 2 and a seal ring 5 fixed to arotating shaft 4 which is inserted through the seat ring 3, the sealring 5 being adapted to rotate together with the rotating shaft 4. On asliding surface 5a of the seal ring 5 there are formed fine grooves 6which are inclined rearwardly in the diametrical direction of thesliding surface 5a with respect to the rotational direction (arrow B) ofthe seal ring 5, and also fine grooves 7 which are inclined forwardly,both ends of the fines grooves 6 and 7 respectively reaching the outerperipheral end 5b and the inner peripheral end 5c of the sliding surface5a so that the fine grooves 6 and 7 cross each other. The forwardlyinclined fine grooves 7 function to form a lubricating fluid film on thesliding surface 5a (lubricating function), while the rearwards inclinedfine grooves 6 function to seal fluid by utilization of a pumping action(sealing function). As shown on a larger scale in FIG. 3, the sealingfluid (A) is introduced into the fine grooves 7 by virtue of therotation of the sliding surface 5a and of its viscous action, then moveswhile staying in the fine grooves 7 and forms a lubricating fluid filmthereby providing lubricating between the sliding surface 5a of the sealring 5 and the sliding surface 3a of the seat ring 3. The sealing fluid(A) which has moved along the forwardly inclined fine grooves 7 is thentransferred into the rearwardly inclined fine grooves 6 at the pointswhere the fine grooves 6 and 7 cross each other, so that the fluid (A)is discharged to the intake (the outer peripheral end 5b side) withoutreaching the inner peripheral end 5c of the sliding surface 5a. In thisembodiment, therefore, the forwardly inclined fine grooves 7 and therearwardly inclined fine grooves 6 may be formed so as to afford adischarge capacity surpassing the amount of fluid introduced between thesliding surfaces 3a and 5a, that is, in such a manner that the dischargecapacity of the rearwardly inclined fine grooves 6 surpasses the intakecapacity of the forwardly inclined fine grooves 7. In other words, thenumber, shape or direction of the rearwardly inclined fine grooves 6becomes predominant. In this case, for completely preventing the leakageof fluid through the mechanical seal 1 while the machine is not inoperation, it is necessary to prevent the outflow from the fine grooves6 and 7, and this purpose can be attained by finishing the fine grooves6 and 7 within 0.2μ to 0.7μ. In case a certain degree of leakage isallowed, when the time of shut down is short, or in case fluid does notcome to the mechanical seal portion or pressure is released during shutdown of the machine, the fine grooves 6 and 7 may be finished up to 1.0μto 3μ, within which range there can be obtained an ordinary sealingeffect. Thus, the fine grooves 6 and 7 are controlled within the rangeof from 0.2μ to 3μ according to their purposes.

In the mechanical seal 1 having the above construction, the fine grooves6 and 7 required to control the flow rate are formed on the slidingsurface 5a of the seal ring 5, and it is desirable that those finegrooves be formed in the following manner.

According to a first method, the fine grooves 6 and 7 which have beendesigned in advance according to their purpose of use are photo-printedon the sliding surface 5a of the seal ring 5 onto which surface has beenapplied a photosensitive material in advance, followed by etching toform the fine grooves 6 and 7 on the sliding surface 5a.

According to a second method, the fine grooves 6 and 7 which have beendesigned in advance according to their purpose of use are stamped orprinted with ink on the sliding surface 5a of the seal ring 5, followedby etching to form the fine grooves 6 and 7 on the sliding surface 5a.

According to a third method, the fine grooves 6 and 7 are formed byapplying marking-off to the sliding surface 5a which has been subjectedto a grinding or lapping process. It is preferable that the fine grooves6 and 7 thus formed by this marking-off process be then subjected topolishing. As a result, the cross-sectional shape of the fine grooves 6and 7 becomes as shown in FIG. 4, that is, swollen portions 8 are formedat both edges of the fine grooves 6 and 7 whereby a lubricating fluidfilm is easily formed on the sliding surface 5a, and this effect ispeculiar to the method of this invention.

Thus, according to the aforesaid methods for forming the slidingsurface, any shape and any number of the fine grooves 6 and 7 can beformed with a very high accuracy within the range capable of being shownin a design drawing, and as shown in FIGS. 5 through 7 the balancebetween the amount of leakage and the durability required of themechanical seal 1 can be maintained so as to give the best sealingdurability at all times by suitably selecting the relative constructionof the rearwardly inclined fine grooves 6 and the forwardly inclinedfine grooves 7.

FIG. 8 is an experimental graph showing the relationship between thenumber of the fine grooves 6 and 7 and the amount of leakage, from whichit is clearly seen that both are correlated with each other. In thisexperiment, the number of the rearwardly inclined fine grooves 6 wasfixed at 16, while the number of the forwardly inclined fine grooves 7was changed gradually. The shaft revolution and fluid pressure were5,000 rpm and 6 kg/cm.G, respectively.

In the foregoing description, the mechanical seal 1 was of the externalpressure type and the fine grooves 6 and 7 were formed on the slidingsurface 5a of the seal ring 5 of the mechanical seal 1. In thisinvention, however, without being limited to such a construction, themechanical seal 1 may be made of the internal pressure type and the finegrooves 6 and 7 may be formed on the sliding surface 3a of the seat ring3 of the mechanical seal 1. In this case, however, the forwardlyinclined fine grooves 7 come to exhibit a sealing effect and therearwardly inclined fine grooves 6 exhibit a lubricating effect;therefore, as shown in FIG. 9, the number of the fine grooves 6 and thatof the fine grooves 7 required with respect to the relative rotationaldirection (arrow B) are reversed. As illustrated, moreover, the planarshape of the fine grooves 6 and 7 may be rectilinear, curvilinear, or amixed form of both straight and curved lines.

While preferred embodiments of this invention have been described, it isobvious that various other modifications and changes may be made withoutdeparting from the principle of the invention. Therefore, it is intendedto cover in the appended claims all modifications and changes whereinthe effects of the invention are substantially obtainable through theuse of constructions substantially the same as or falling under thescope of the invention.

We claim:
 1. A mechanical seal comprising a seat ring fixed to ahousing, a seal ring fixed to a rotating shaft, said seal ring rotatingwith said rotating shaft, said seat ring and said seal ring being insliding contact with each other to prevent the leakage of fluid, and aplurality of fine grooves formed on a sliding surface of one of saidrings, some of said fine grooves being inclined forwardly for performinga lubricating action and the remainder being inclined rearwardly toperform a pumping action, said grooves being inclined forwardly andrearwardly with respect to the relative rotational direction of saidseal ring, each of said fine grooves respectively having ends extendingto the outer peripheral edge and the inner peripheral edge of saidsliding surface, said forwardly inclined grooves and said rearwardlyinclined grooves intersecting one another such that sealing fluid ispassable from said forwardly inclined grooves to said rearwardlyinclined grooves at said intersections such that sealing fluid enterssaid seal via said forwardly inclined grooves and exits said seal viasaid rearwardly inclined grooves, said rearwardly inclined grooves beinggreater in number than said forwardly inclined grooves such that thedischarge capacity resulting from said pumping action of said rearwardlyinclined grooves is greater than the intake capacity of said forwardlyinclined grooves.
 2. A mechanical seal according to claim 1, whereinsaid grooves are non-radially disposed.
 3. A mechanical seal accordingto claim 1, wherein said forwardly inclined grooves have their outerradial ends disposed circumferentially forward of the respective innerradial ends considered in the direction of rotation of said seal ring.4. A mechanical seal according to claim 1, wherein said rearwardlyinclined grooves have their outer radial ends disposed circumferentiallyrearwardly of the respective inner radial ends considered in thedirection of rotation of said seal ring.
 5. A mechanical seal accordingto claim 1 wherein said seal is of the external pressure type whereinthe pressure fluid being sealed is disposed radially outwardly of theseal.
 6. A mechanical seal according to claim 1 wherein at least some ofsaid grooves are formed along straight lines.
 7. A mechanical sealaccording to claim 1 wherein at least some of said grooves are formedalong curvilinear lines.
 8. A mechanical seal according to claim 1wherein at least some of said grooves are formed along both straightlines and curvilinear lines.
 9. A mechanical seal according to claim 1,wherein said fine grooves have a maximum cross sectional dimensionwithin the range of 0.2μ to 3μ.
 10. A mechanical seal according to claim1 wherein said fine grooves have a maximum cross sectional dimensionwithin the range of 0.2μ to 0.7μ.
 11. A mechanical seal according toclaim 1 wherein said fine grooves have a maximum cross sectionaldimension with the range of 1.0μ to 3μ.
 12. A mechanical seal comprisinga seat ring fixed to a housing, a seal ring fixed to a rotating shaft,said seal ring rotating with said rotating shaft, said seat ring andsaid seal ring being in sliding contact with each other to prevent theleakage of fluid, and a plurality of fine grooves formed on a slidingsurface of one of said rings, some of said fine grooves being inclinedrearwardly for performing a lubricating action and the remainder beinginclined forwardly to perform a pumping action, said grooves beinginclined forwardly and rearwardly with respect to the relativerotational direction of said sliding surface, each of said fine groovesrespectively having ends reaching the outer peripheral edge and theinner peripheral edge of said sliding surface, said rearwardly inclinedgrooves and said forwardly inclined grooves intersecting one anothersuch that sealing fluid is passable from said rearwardly inclinedgrooves to said forwardly inclined grooves at said intersections suchthat sealing fluid enters said seal via said rearwardly inclined groovesand exits said seal via said forwardly inclined grooves, said forwardlyinclined grooves being greater in number than said rearwardly inclinedgrooves such that the discharge capacity of said forwardly inclinedgrooves is greater than the intake capacity of said rearwardly inclinedgrooves.
 13. A mechanical seal according to claim 12, wherein saidgrooves are non-radially disposed.
 14. A mechanical seal according toclaim 12 wherein said seal is of the internal pressure type wherein thepressure fluid being sealed is disposed radially inwardly the seal. 15.A mechanical seal according to claim 12 wherein at least some of saidgrooves are formed along straight lines.
 16. A mechanical seal accordingto claim 12 wherein at least some of said grooves are formed alongcurvilinear lines.
 17. A mechanical seal according to claim 12 whereinat least some of said grooves are formed along both straight lines andcurvilenear lines.
 18. A mechanical seal according to claim 12 whereinsaid fine grooves have a maximum cross sectional dimension within therange of 0.2μ to 3μ.